Comparison of BSD operating systems
There are a number of Unix-like operating systems based on or descended from the Berkeley Software Distribution (BSD) series of Unix variants options. The three most notable descendants in current use are FreeBSD, OpenBSD, and NetBSD, which are all derived from 386BSD and 4.4BSD-Lite, by various routes. Both NetBSD and FreeBSD started life in 1993, initially derived from 386BSD, but in 1994 migrating to a 4.4BSD-Lite code base. OpenBSD was forked from NetBSD in 1995. Other notable derivatives include DragonFly BSD, which was forked from FreeBSD 4.8, and Apple Inc.'s iOS and macOS, with its Darwin base including a large amount of code derived from FreeBSD.
Most of the current BSD operating systems are open source and available for download, free of charge, under the BSD License, the most notable exceptions being macOS and iOS. They also generally use a monolithic kernel architecture, apart from macOS, iOS, and DragonFly BSD which feature hybrid kernels. The various open source BSD projects generally develop the kernel and userland programs and libraries together, the source code being managed using a single central source repository.
In the past, BSD was also used as a basis for several proprietary versions of UNIX, such as Sun's SunOS, Sequent's Dynix, NeXT's NeXTSTEP, DEC's Ultrix and OSF/1 AXP (which became the now discontinued Tru64 UNIX). Parts of NeXT's software became the foundation for macOS which, together with iOS, is among the most commercially successful BSD variants in the general market.
Aims and philosophies
DragonFly BSD aims to be inherently easy to understand and develop for multi-processor infrastructures. The main goal of the project, forked from FreeBSD 4.8, is to radically change the kernel architecture, introducing microkernel-like message passing which will enhance scaling and reliability on symmetric multiprocessing platforms while also being applicable to NUMA and clustered systems. The long-term goal is to provide a transparent single system image in clustered environments. DragonFly BSD originally supported both the IA-32 and x86-64 platforms, however support for IA-32 was dropped in version 4.0. Matthew Dillon, the founder of DragonFly BSD, believes supporting fewer platforms makes it easier for a project to do a proper, ground-up SMP implementation.
FreeBSD aims to make an operating system usable for any purpose. It is intended to run a wide variety of applications, be easy to use, contain cutting edge features, and be highly scalable on very high load network servers. FreeBSD is free software, and the project prefers the FreeBSD license. However, they sometimes accept non-disclosure agreements (NDAs) and include a limited number of nonfree hardware abstraction layer (HAL) modules for specific device drivers in their source tree, to support the hardware of companies who do not provide purely libre drivers (such as HALs to program software-defined radios so that vendors do not share their nonfree algorithms). To maintain a high level of quality and provide good support for "production quality commercial off-the-shelf (COTS) workstation, server, and high-end embedded systems", FreeBSD focuses on a narrow set of architectures. A significant focus of development since 2000 has been fine-grained locking and SMP scalability. From 2007 on, most of the kernel was fine-locked and scaling improvements started to be seen. Other recent work includes Common Criteria security functionality, such as mandatory access control and security event audit support.
- TrueOS (previously PC-BSD) - open source FreeBSD based desktop operating system aiming at user friendliness for the UNIX-like laypeople. KDE was the default desktop environment up to PC-BSD8, but as of PC-BSD9 a range of environments including KDE, Xfce, GNOME, and Fluxbox, and many window managers are available to choose from during the installation. An easy to use software manager is included, which downloads and installs binary packages in TrueOS's own .pbi format. Each version of TrueOS remains directly descended from the same version of FreeBSD. For security reasons TrueOs (like OpenBSD) uses LibreSSL, instead of the standard out of the box OpenSSL that FreeBSD comes with.
NetBSD aims to provide a freely redistributable operating system that professionals, hobbyists, and researchers can use in any manner they wish. The main focus is portability, through the use of clear distinctions between machine-dependent and machine-independent code. It runs on a wide variety of 32-bit and 64-bit processor architectures and hardware platforms, and is intended to interoperate well with other operating systems. NetBSD places emphasis on correct design, well-written code, stability, and efficiency. Where practical, close compliance with open API and protocol standards is also aimed for. In June, 2008, the NetBSD Foundation moved to a two-clause BSD license, citing changes at UCB and industry applicability. NPF is a project spawned by NetBSD.
OpenBSD is a security-focused BSD known for its developers' insistence on extensive, ongoing code auditing for security and correct functionality, a "secure by default" philosophy, good documentation, and adherence to strictly open source licensing. The system incorporates numerous security features that are absent or optional in other versions of BSD. The OpenBSD policy on openness extends to hardware documentation and drivers, since without these, there can be no trust in the correct operation of the kernel and its security, and vendor software bugs would be hard to resolve.
OpenBSD emphasizes very high standards in all areas. Security policies include disabling all non-essential services and having sane initial settings; and integrated cryptography (originally made easier due to relaxed Canadian export laws relative to the United States), full public disclosure of all security flaws discovered; thoroughly auditing code for bugs and security issues; various security features, including the W^X page protection technology and heavy use of randomization to mitigate attacks. Coding approaches include an emphasis on searching for similar issues throughout the code base if any code issue is identified. Concerning software freedom, OpenBSD prefers the BSD or ISC license, with the GPL acceptable only for existing software which is impractical to replace, such as the GNU Compiler Collection. NDAs are never considered acceptable. In common with its parent, NetBSD, OpenBSD strives to run on a wide variety of hardware. Where licenses conflict with OpenBSD's philosophy, the OpenBSD team has re-implemented major pieces of software from scratch, which have often become the standard used within other versions of BSD. Examples include the pf packet filter, new privilege separation techniques used to safeguard tools such as tcpdump and tmux, much of the OpenSSH codebase, and replacing GPL licensed tools such as diff, grep and pkg-config with ISC or BSD licensed equivalents.
OpenBSD prominently notes the success of its security approach on its website home page. As of April 2018, only two vulnerabilities have ever been found in its default install (an OpenSSH vulnerability found in 2002, and a remote network vulnerability found in 2007) in a period of almost 22 years. According to OpenBSD expert Michael W. Lucas, OpenBSD "is widely regarded as the most secure operating system available anywhere, under any licensing terms."
In September 2005, the BSD Certification Group, after advertising on a number of mailing lists, surveyed 4,330 BSD users, 3,958 of whom took the survey in English, to assess the relative popularity of the various BSD operating systems. About 77% of respondents used FreeBSD, 33% used OpenBSD, 16% used NetBSD, 2.6% used Dragonfly, and 6.6% used other (potentially non-BSD) systems. Other languages offered were Brazilian and European Portuguese, German, Italian, and Polish. Note that there was no control group or pre-screening of the survey takers. Those who checked "Other" were asked to specify that operating system.
Because survey takers were permitted to select more than one answer, the percentages shown in the graph, which are out of the number survey of participants, add up to greater than 100%. If a survey taker filled in more than one choice for "other", this is still only counted as one vote for other on this chart.
Another attempt to profile worldwide BSD usage is the *BSDstats Project, whose primary goal is to demonstrate to hardware vendors the penetration of BSD and viability of hardware drivers for the operating system. The project collects data monthly from any BSD system administrators willing to participate, and currently records the BSD market share of participating FreeBSD, OpenBSD, NetBSD, DragonflyBSD, Debian GNU/kFreeBSD, TrueOS, and MirBSD systems.
DistroWatch, well known in the Linux community and often used as a rough guide to free operating system popularity, publishes page hits for each of the Linux distributions and other operating systems it covers. As of 4 September 2016, using a data span of the last six months it placed FreeBSD in 21st place with 479 hits per day; TrueOS in 46th place with 244 hits per day; GhostBSD in 47th place with 242 hits, OpenBSD in 75th place with 163 hits per day; MidnightBSD in 118th place with 89 hits per day; and NetBSD in 142nd place with 66 hits per day.
Names, logos, slogans
The first BSD mascot was the BSD daemon, named after a common type of Unix software program, a daemon. FreeBSD still uses the image, a red cartoon daemon named Beastie, wielding a pitchfork, as its mascot today. In 2005, after a competition, a stylized version of Beastie's head designed and drawn by Anton Gural was chosen as the FreeBSD logo. The FreeBSD slogan is "The Power to Serve."
The NetBSD flag, designed in 2004 by Grant Bisset, is inspired by the original NetBSD logo, designed in 1994 by Shawn Mueller, portraying a number of BSD daemons raising a flag on top of a mound of computer equipment. This was based on a World War II photograph, Raising the Flag on Iwo Jima. The Board of Directors of The NetBSD Foundation believed this was too complicated, too hard to reproduce and had negative cultural ramifications and was thus not a suitable image for NetBSD in the corporate world. The new, simpler flag design replaced this. The NetBSD slogan is "Of course it runs NetBSD", referring to the operating system's portability.
Originally, OpenBSD used the BSD daemon as a mascot, sometimes with an added halo as a distinguishing mark, but OpenBSD later replaced its BSD daemon with Puffy. Although Puffy is usually referred to as a pufferfish, the spikes on the cartoon images give him a closer likeness to the porcupinefish. The logo is a reference to the fish's defensive capabilities and to the Blowfish cryptography algorithm used in OpenSSH. OpenBSD also has a number of slogans including "Secure by default", which was used in the first OpenBSD song, "E-railed", and "Free, Functional & Secure", and OpenBSD has released at least one original song with every release since 3.0.
The DragonFly BSD logo, designed by Joe Angrisano, is a dragonfly named Fred. A number of unofficial logos by various authors also show the dragonfly or stylized versions of it. DragonFly BSD considers itself to be "the logical continuation of the FreeBSD 4.x series." FireflyBSD has a similar logo, a firefly, showing its close relationship to DragonFly BSD. In fact, the FireflyBSD website states that proceeds from sales will go to the development of DragonFly BSD, suggesting that the two may in fact be very closely related.
PicoBSD's slogan is "For the little BSD in all of us," and its logo includes a version of FreeBSD's Beastie as a child, showing its close connection to FreeBSD, and the minimal amount of code needed to run as a Live CD.
A number of BSD OSes use stylized version of their respective names for logos. This includes macOS, TrueOS, GhostBSD, DesktopBSD, ClosedBSD, and MicroBSD. TrueOS's slogan is "Personal computing, served up BSD style!", GhostBSD's "A simple, secure BSD served on a Desktop." DesktopBSD's "A Step Towards BSD on the Desktop." MicroBSD's slogan is "The small secure unix like OS."
MirOS's site collects a variety of BSD mascots and Tux, the Linux mascot, together, illustrating the project's aim of supporting both BSD and Linux kernels. MirOS's slogan is "a wonderful operating system for a world of peace."
|Primary developers||First public release||Based on||Latest stable version||Cost (USD)||Preferred license||Purpose||Short description|
|FreeBSD||The FreeBSD Project||1993-12-01||386BSD, 4.4BSD-Lite||11.2||2018-06-21||Free||Simplified BSD||Server, Workstation, Network Appliance, Embedded||Aims to be usable for any purpose.|
|OpenBSD||The OpenBSD Project||1996-09-01||NetBSD 1.0||6.3||2018-04-15||Free||ISC||Server, Workstation, Network Appliance, Embedded||Aims for maximum correctness in code, bringing simplicity and security.|
|NetBSD||The NetBSD Project||1993-05-01||386BSD, 4.4BSD-Lite||8.0||2018-07-21||Free||Simplified BSD||Server, Workstation, Network Appliance, Embedded||Aims for maximum portability.|
|DragonFly BSD||Matt Dillon||2004-07-12||FreeBSD 4.8||5.2.2||2018-06-18||Free||Modified BSD||Server, Workstation, Network Appliance, Embedded||Aims for maximum scalability.|
|386BSD||William and Lynne Jolitz||1992-03-01||4.3BSD Net/2||1.0||1994-11-01||Free||BSD||Open source general purpose||Historical|
|BSD/OS (BSD/386)||BSDi, Wind River Systems||1993-03-01||4.3BSD Net/2, 4.4BSD||5.1||2003-10-01||?||Proprietary||General purpose||Historical|
|SunOS||Sun Microsystems||1982||4.xBSD, UNIX System V||4.1.4||1994-11-01||Included in hardware and support charges||Proprietary||Server, Workstation||Historical (Solaris is a different code base)|
|Ultrix||Digital Equipment Corporation||1984||4.2BSD, SVR2||4.5||1995||?||Proprietary||General Purpose||Historical (ran on DEC VAX & MIPS systems or emulators).|
|RISCiX||Acorn Computers||1988||4.3 BSD, Unix System V||1.31c||1993-09-07||Non-free £1000 GBP (Approx $1400)||Proprietary||Workstation||Historical (ran on Archimedes and R series Workstations)|
|Tru64 UNIX (DEC OSF/1, Digital UNIX)||DEC, Compaq, HP||1993||4.3BSD, 4.4BSD, Mach 2.5, UNIX System V||5.1B-6||2010-10-01||Non-free $99 (non-commercial)||Proprietary||General Purpose||Only runs on HP Alpha systems or emulators.|
|macOS||Apple Inc.||2001-03-24||Darwin||10.13 "High Sierra"||2017-09-25||Client: Free
Server (add-on application): $19.99
|Open source core system (see Darwin) with proprietary higher level API layers locking to Apple hardware||Workstation, Home Desktop, Server||Locked to Apple hardware use only|
|iOS||Apple Inc.||2007-06-01||Darwin||11.2||2017-12-04||Free||Open source core system (see Darwin) with proprietary higher level API layers locking to Apple hardware||Embedded mobile device||Ships with Apple iPhone, iPad, iPod Touch, Apple TV, Apple Watch|
|Darwin||Apple Inc.||2001-03-01||NeXTSTEP, FreeBSD, classic Mac OS||17.0.0||2017-09-19||Free||APSL, GPL and others||Workstation, Home Desktop, Server||The kernel and certain userland components of macOS and iOS|
|TrueOS||iXsystems, Inc.||2006-04-29||FreeBSD||18.3||2018-03-30||Free||BSD||Desktop||Easy to use while maintaining full use of FreeBSD base|
|GhostBSD||Eric Turgeon||2009-11-01||FreeBSD||11.1||2017-11-16||Free||BSD||Desktop, Workstation||Easy to use, full FreeBSD w/ GNOME, Mate, Xfce, LXDE or Openbox.|
|DesktopBSD||Peter Hofer, Daniel Seuffert||2005-07-25||FreeBSD||1.7||2009-09-07||Free||BSD||Desktop||Easy to use|
|ClosedBSD||Joshua Bergeron and various contributors||?||FreeBSD||1.0B (floppy), 1.0-RC1 (CD)||?||Free||Proprietary||?||firewall/NAT, boot floppy, Live CD|
|FreeSBIE||?||?||FreeBSD||2.0.3||2007-02-01||Free||?||?||Live CD of FreeBSD. DistroWatch lists as discontinued.|
|PicoBSD||Michael Bialecki||?||FreeBSD||0.42||?||Free||BSD||boot floppy||?|
|Anonym.OS||?||2005-01-01||OpenBSD 3.8||none (beta only)||?||Free||?||Anonymous browsing||Live CD|
|MirOS BSD||The MirOS Project||?||OpenBSD 3.1||#10||2008-03-16||Free||?||?||European|
|ekkoBSD||Rick Collette||?||OpenBSD 3.3||?||?||?||?||Server||easy to administer|
|MicroBSD||Bulgarians||?||OpenBSD 3.0/3.4||0.6||2003-10-27||Free||?||General purpose||Small, secure|
|OliveBSD||Gabriel Paderni||?||OpenBSD 3.8||?||?||Free||?||Live CD||DistroWatch lists as discontinued.|
|Gentoo/FreeBSD||Gentoo Linux developers||?||FreeBSD||?||?||Free||GPL, BSD||Server, Workstation, Network Appliance||uses Gentoo framework|
|Gentoo/OpenBSD||Gentoo Linux developers||?||OpenBSD||?||?||Free||GPL, BSD||Server, Workstation, Network Appliance, Embedded||uses Gentoo framework|
|Gentoo/NetBSD||Gentoo Linux developers||?||NetBSD||?||?||Free||GPL, BSD||Server, Workstation, Network Appliance, Embedded||uses Gentoo framework|
|Gentoo/DragonflyBSD||Robert Sebastian Gerus (project not yet officially supported by Gentoo)||?||DragonFly BSD||?||?||Free||?||Server, Workstation, Network Appliance||uses Gentoo framework|
|Debian GNU/kFreeBSD||The Debian GNU/kFreeBSD team||2011-02-06||GNU, FreeBSD||7.5||2014-04-26||Free||DFSG||General purpose||GNU userspace on FreeBSD kernel|
|Debian GNU/NetBSD||The Debian GNU/kNetBSD team||Abandoned||GNU, NetBSD||Abandoned||Abandoned||Free||DFSG||General purpose||GNU userspace on NetBSD kernel|
|MidnightBSD||Lucas Holt||2007-08-04||FreeBSD 6.1 beta||0.8.6||2017-08-28||Free||BSD||Desktop||GNUstep based Desktop Environment|
|pfSense||various contributors||2006-10-04||FreeBSD||2.4.3||2018-03-29||Free||BSD||Security appliance||firewall/NAT, Live CD|
|Paxym FreeBSD for Octeon||Paxym Inc.||2007-12-11||FreeBSD 7.0||4.7||2008-08-13||?||Proprietary||Network, Storage, Security Applications: Routers/UTM/Firewall/NAS||For Cavium Networks Octeon MIPS architecture multicore processors|
|MaheshaBSD||?||FreeBSD 8||?||?||Free||BSD||FreeBSD multipurpose|
|?||?||Free||Free software||FreeBSD, OpenBSD Firewall, MP3 player, backup, others|
|Jibbed||OpenBSD, NetBSD||6.0||Free||BSD||Live CD of NetBSD|
|Bitrig||The Bitrig Developers||2014-11-25||OpenBSD||1.0||2014-11-25||Free||ISC||General Purpose||Focus on modern platforms and tools|
|Developer||First public release||Based on||Version||Release Date||Cost (USD)||Preferred license||Purpose||Short description|
- 386BSD, BSD/OS, SunOS, and Ultrix are historic operating systems that are no longer developed. BSDeviant and ekkoBSD do not exist anymore either, although BSDeviant is still available for download (see external links). MicroBSD ended, then started again in 2003, but it does not seem that any progress has been made since then, though the website still exists.
- This article only refers to SunOS through version 4.x. SunOS from release 5.x forward is based on SVR4, and is most commonly referred to as Solaris.
Notes and references
- "DragonFly Frequently Asked Questions". The DragonFly BSD Project. Archived from the original on 2006-06-15. Retrieved 2006-07-01.
- "DragonFlyBSD: FAQ-English". The DragonFly BSD Project. Retrieved 2014-12-24.
- Biancuzzi, Federico (2004-07-08). "Behind DragonFly BSD An Interview with the developers.". O’Reilly Media, Inc. p. 3. Retrieved 2006-04-29.
- "Chapter 1 Introduction: 1.2. - What is the goal of the FreeBSD Project?". Frequently Asked Questions for FreeBSD 4.X, 5.X, and 6.X. The FreeBSD Documentation Project. 1995–2006. Retrieved 2006-04-22.
- "About FreeBSD". The FreeBSD Project. 2006-10-12. Retrieved 2006-10-14.
- "Support for Multiple Architectures: Statement of General Intent". Committer's Guide. The FreeBSD Documentation Project. Retrieved 2006-10-14.
The FreeBSD Project targets "production quality commercial off-the-shelf (COTS) workstation, server, and high-end embedded systems".
- "Destabilization due to SMP development". Retrieved 27 May 2015.
- Moore, Kris (March 14, 2011). "A Quick Look at the Upcoming PC-BSD 9". Official PC-BSD Blog. Retrieved November 21, 2011.
- "About the NetBSD Project - What is the NetBSD project?". The NetBSD Foundation, Inc. 2006-01-08. Retrieved 2006-04-22.
- de Raadt, Theo (5 December 2006). "Presentation at OpenCON". OpenBSD. Retrieved 13 December 2011.
- "OpenBSD Project Goals". OpenBSD. 2005-10-12. Retrieved 2006-04-22.
- Lucas, Michael W. (2013). Absolute OpenBSD: Unix for the practical paranoid (2nd ed.). San Francisco: No Starch Press. p. xxix. ISBN 978-1-59327-476-4.
- "Faq - Bitrig", Github, 7 December 2014.
- BSD Certification site; PDF of usage survey results. Retrieved on 2012-09-16.
- "*BSD Usage Statistics". The *BSD Stats Project. Retrieved 2006-09-30.
- "DistroWatch.com: Put the fun back into computing". DistroWatch.com. 2001–2011. Retrieved 2016-09-04.
- "Chapter 1 Introduction - Why is it called FreeBSD?". Frequently Asked Questions for FreeBSD 4.X, 5.X, and 6.X. The FreeBSD Documentation Project. 1995–2006. Retrieved 2006-06-11.
- "About the NetBSD Project - Why the name?". The NetBSD Foundation. 1994–2006. Retrieved 2006-12-06.
- FreeBSD Logo Competition. The FreeBSD Project. Competition ended 2005-06-30. Retrieved on 2006-04-22.
- Mueller, Shawn (1994). "Original NetBSD Logo" (JPEG). The NetBSD Foundation. Retrieved 2006-04-22. Also see NetBSD Logos.
- Mewburn, Luke (2004-01-14). "NetBSD logo design competition". Netbsd-advocacy mailing list. Retrieved 2006-04-22.
Linked to from:
"Changes and NetBSD News in 2004 - NetBSD Logo Design Contest". The NetBSD Foundation, Inc. 2004-01-13. Retrieved 2006-10-14.
"The NetBSD Foundation Press Release: Announcement of New Logo - NetBSD has a new logo!". The NetBSD Foundation, Inc. 2004-10-30. Retrieved 2006-04-22.
- "OpenBSD 3.9 - Free, Functional & Secure" (JPEG). OpenBSD. Retrieved 2006-07-01.
- "OpenBSD release song lyrics". OpenBSD. 2006-04-15. Retrieved 2006-04-22.
- official DragonFlyBSD artwork
- "DFWiki - DragonFly Artwork". The DragonFlyBSD Project. 2006-03-28. Archived from the original on 2005-04-10. Retrieved 2006-04-22.
- "The History of DragonFly". The DragonFly BSD Project. Archived from the original on 2006-04-14. Retrieved 2006-04-22.
- "PicoBSD Banner - For the little BSD in all of us". The FreeBSD Project. Archived from the original (GIF) on 2006-05-03. Retrieved 2006-04-22.
- "ClosedBSD logo". Archived from the original (JPEG) on 2005-03-06. Retrieved 2006-10-14. Original last retrieved on 2006-04-22.
- "MicroBSD logo - The small secure unix like OS" (PNG). Retrieved 2006-04-22.
- "MirOS/MirPorts: a wonderful operating system for a world of peace". MirOS Project. Retrieved 2006-04-22.
- "SunOS 4.1.3: svidii - overview of the System V environment". FreeBSD Hypertext Man Pages. The FreeBSD Project. 1989-09-30. Retrieved 2006-06-14.
- "MidnightBSD News". Retrieved 27 May 2015.
- "About MidnightBSD". Retrieved 27 May 2015.
- "Paxym - FreeBSD for OCTEON CPU". Retrieved 27 May 2015.
- "One Floppy OpenBSD MP3 Player". Retrieved 27 May 2015.
- Milo; et al. (1998-06-22). "FreeBSD". Operating System Technical Comparison. OSdata. Archived from the original on 2007-01-14. Retrieved 2006-06-02.
- Milo; et al. (1998-06-22). "OpenBSD". Operating System Technical Comparison. Retrieved 2006-06-02.
- Milo; et al. (1998-06-22). "NetBSD". Operating System Technical Comparison. OSdata. Retrieved 2006-06-02.
- Milo; et al. (1998-06-22). "SunOS". Operating System Technical Comparison. OSdata. Retrieved 2006-06-02.
- "SunOS & Solaris version history". Berkeley. Archived from the original on 2006-02-09. Retrieved 2006-06-02.
- "Ultrix FAQ". 1996-11-04. Archived from the original on 2006-05-19. Retrieved 2006-06-02.
- Milo ' (1998-06-22). "Ultrix". Operating System Technical Comparison. OSdata. Retrieved 2006-06-02.
- Milo; et al. (1998-06-22). "Mac OS X". Operating System Technical Comparison. OSdata. Retrieved 2006-06-02.
- Milo; et al. (1998-06-22). "Mac OS X Server". Operating System Technical Comparison. OSdata. Archived from the original on 2007-01-14. Retrieved 2006-06-02.
- "BSDeviant download page". Bsdeviant.org. Retrieved 2008-06-30. A semi-official download page.
- "ekkoBSD 1.0 BETA1B Released". Slashdot. 2003-11-25. Retrieved 2006-06-03.
- Milo; et al. (1998-05-31). "Operating System Technical Comparison". OSdata. Retrieved 2006-06-02.
- Brown, Martin (2004-08-10). "Differentiating Among BSD Distros". Jupitermedia Corporation. p. 4. Retrieved 2006-06-03.
- Schneider, Wolfram; Gilliam, Josh; Schultz, Steven M. (1997–2004). "The UNIX system family tree: Research and BSD" (ASCII). The NetBSD Foundation. Retrieved 2006-06-03.